Field of the Invention
The present invention relates to hydrocarbon fluids, particularly hydrocarbon fluids for formulating wellbore fluids used in oil and gas well operations such as drilling, hydraulic fracturing, gravel packing, as well as numerous other downhole operations.
Description of the Prior Art
In the process of drilling a well into an oil and gas bearing formation, a drilling fluid or “mud” is pumped into the developing wellbore through the drill pipe and exits through nozzles in the rotating drill bit mounted at the end of the drill pipe. The drilling fluid is then circulated back to the surface through the annulus, the space between the drill pipe and the wall of the wellbore. Back at the surface, solids are removed and the mud is pumped to a fluid tank where it can be reused or treated if necessary. The drilling fluid system is typically designed as a loop with the drilling fluids continually circulating as the drill bit rotates. Drilling fluid performs several functions essential to the successful completion of an oil or gas well and enhances the overall efficiency of the drilling operation. Drilling fluid is used, for instance, to cool and lubricate the rotating drilling tool, to reduce friction between the bit and the wellbore, to prevent sticking of the drill pipe, to control subsurface pressure in the wellbore, to lift the drill cuttings and carry them to the surface, and to clean the wellbore and drilling tool.
The major component of drilling fluid is its base fluid. A drilling fluid may be aqueous based, hydrocarbon based, synthetic based, or an emulsion, such as an oil-in-water or water-in-oil (“invert”) emulsion. Aqueous based, or water based, drilling fluids are used frequently in the industry. They provide an economic advantage over oil based drilling fluids and are also more environmentally friendly. However, for certain formations, drilling with aqueous based fluids can be problematic due to wellbore instability caused by the swelling of water-absorbing rock and clay in the formation, hydration of which can be greatly reduced by using an oil based drilling fluid. Although oil based fluids are more costly than aqueous based fluids, they are generally preferred for deep drilling, high temperature drilling or when a substantially non-reactive base fluid is required for a particular drilling operation or formation. Oil based fluids tend to provide more natural lubrication than water based fluids and achieve greater increases in drilling progress, or increased rates of penetration (ROP).
The better lubricity afforded by hydrocarbon based fluids decreases undesirable torque and drag and is especially important in highly deviated wells e.g., in horizontal wells where friction is a major concern. Horizontal drilling has become increasingly important, particularly in North America in so-called shale plays. In fact, a recent industry publication suggested that in the United States, six of every ten active rigs were drilling horizontally in any given week. Accordingly, even though hydrocarbon based fluids are more expensive, the results they achieve in turns of ROP, reduced torque and drag makes them economically attractive in horizontal drilling.